Don't Mess with Cthulhu is a social deduction game with secret identities. Players are either Investigators trying to keep Cthulhu from waking and controlling the world, or Cultists that want to bring the world to a disturbing end.

The game takes place over four rounds. The Investigators must uncover all the Elder Signs to win; the Cultists win when Cthulhu is revealed or if the game ends before all the Elder Signs are discovered.